1. Field of the Invention
This invention relates to a failure diagnosis device of an EGR (exhaust gas recirculation) control device utilized in an internal combustion engine and the like.
2. Discussion of Background
An example of a conventional failure diagnosis device of an EGR control device is shown in Japanese Unexamined Patent Publication No. 51746/1987. In this conventional example, the failure diagnosis is performed by forcibly making the EGR from ON to OFF when the failure diagnosis is performed, in a domain wherein the EGR control device is operated (recirculates EGR gas in an internal combustion engine). When the EGR is normal, and the EGR is made OFF, lowering of a pressure in an intake pipe, shortening of a basic fuel injection time calculated by a change of the intake pipe pressure and a variation of an air fuel ratio from RICH to LEAN, or the like are caused. When these changes of state are not caused, the EGR is determined to be abnormal, and an alarm is issued to a driver.
The conventional failure diagnosis device of an EGR control device is composed as above, wherein it is necessary to make temporarily and forcibly OFF the EGR, and a temporary change of the intake pipe pressure causes a variation in torque of the engine, which gives shock (oscillation) to a driver.